The above-identified patent applications describe a standard concrete pump having a hopper adapted to hold the viscous concrete mass and having a front wall formed with a front port at a front axis perpendicular to the front wall at the front port and a rear wall formed with two rear ports centered on respective rear axes perpendicular to the rear wall at the rear ports and generally parallel to the front axis. Respective piston pumps secured to the rear wall outside the hopper over the rear ports can draw portions of the mass out of the hopper and expel the drawn-out portions back into the hopper through the respective rear ports. An outlet conduit is connected to the front wall outside the hopper over the front port.
A nonstraight distributor pipe in the hopper has a front end engaged over and aligned with the front port and a rear end engageable over and alignable with either of the rear ports. The distributor pipe can be pivoted about the front axis between one position with the rear end aligned with and engaged over one of the rear ports and with the other rear port opening into the hopper and another position with the rear end aligned with and engaged over the other rear port and with the one rear port exposed in the hopper.
The hopper is filled with concrete and the pumps are operated alternately, with the one pump expelling concrete into the distributor pipe while the other, whose rear port is exposed in the hopper, draws in a portion. Thus a virtually continuous flow, interrupted only momentarily as the distributor pipe moves between its end positions, is produced in the distributor pipe and outlet conduit connected to it. It is possible in this manner to displace concrete which is an extremely heavy, abrasive, viscous, and corrosive material that either could not be displaced by any conventional pump or that would quickly destroy it.
In order to minimize wear in the distributor pipe, whose ends lie on parallel planes centered on axes that are perpendicular to these planes and offset thereon from each other, this element is S-shaped. Thus losses are minimized as the concrete changes direction in the pipe and the two ends of the distributor pipe are centered on their respective parallel axes. This S-shape may be formed of a succession of straight sections as described in German patent document No. 1,285,319 filed Aug. 8, 1960 by F. W. Schwing, or it may be gently curved as described in German patent document No. 1,653,607 filed by E. L. Sherrod with a claim to the priority of his U.S. application Ser. No. 524,675 filed Feb. 3, 1966.
The distributor pipe can be generally curved and have a generally arcuate centerline crossing the front axis at the front port and extending parallel to the rear axis at the rear wall. This pipe can be wholly curved between its front and rear ends with the centerline smoothly arcuate or it can be formed of two straight portions joined at an elbow. This is made possible by having the outlet pipe extending away from the front wall at an angle, that is with its centerline coaxial with the front end of the front section of the distributor pipe when midway between its positions. The front end of the distributor pipe normally projects axially into a seat so that sealing the joint at this location is easy, and it similarly is no problem to protect the joint from abrasion by the concrete as the distributor pipe oscillates about the front axis. The rear end, however, rides in an arcuate guide slot, engaging backward against a valve plate formed with two holes constituting the rear port. A tight joint is needed here to prevent loss of pumping pressure and to avoid driving water out of the pumped mass.
To this end the distributor pipe is urged backward against the valve plate forming the rear ports, or this valve plate is urged axially forward against the rear end of the distributor pipe. This valve-plate biasing can be effected by springs, or hydraulic cylinders can be employed to allow periodic axial advance of the valve plate as it wears and/or to maintain sufficient pressure to prevent leakage.
German patent document No. 2,162,406 filed Dec. 16, 1971 by K. Schlecht describes a system wherein a C-shaped distributor pipe with both of its ends pointing backwardly is urged axially with a continuous pressure both against the intake ports at the pumps and at the output port. To this end the C-shaped pipe carries a shoe that rides on a traverse provided in the hopper and urged continuously back by an arrangement outside the hopper and connected to the traverse by tie rods that extend through the rear wall into the hopper. In such an arrangement the force is exerted continuously. In addition concrete is constantly present between the shoe carried on the distributor pipe and the traverse-guide on which this shoe rides, so the system is subject to enormous wear.